The present invention relates to a method and an apparatus for controlling a drive unit of a motor vehicle.
In the context of the control of drive units, oscillations occur in the drivetrain in certain operating situations, in particular due to the elasticity of the shafts, and considerably limit the comfort of the vehicle. The oscillations are transmitted to the bodywork, where they result in unpleasant bucking phenomena. One example of these operating states is a load change, for example when pressure on the accelerator pedal is decreased or increased. In the latter case the oscillations have a particularly comfort-impairing effect.
A number of methods are known from the existing art for determining whether such oscillations are present. One example that may be cited here is the method described in German Published Patent Application No. 195 16 120, according to which the presence of drivetrain oscillations is detected by a frequency analysis on the basis of the speed at the differential of the drive axle. In this existing art, the comfort-impairing effects of the drivetrain oscillations are reduced by influencing the activation times of brake pressure control devices.
Also known are actions with which the oscillations that occur are counteracted by intervening in the control system of the drive unit of the vehicle (so-called anti-bucking functions). One example of such a function is known from German Published Patent Application No. 195 23 898. In this, the occurrence of an oscillation is detected by analyzing the engine speed profile; and by influencing the torque of the drive unit, in particular by ignition angle adjustment, the oscillations are counteracted so that the oscillation amplitude is diminished and ideally the oscillation is entirely suppressed. These actions do effectively diminish the oscillations and thus improve vehicle comfort, but the oscillation is simply controlled out without addressing the cause of the oscillations.
German Published Patent Application No. 197 34 112 discloses a method and an apparatus for drive slip control in which, outside the drive slip control context, a maximum drive output torque that can be transmitted to the road in the given circumstances is calculated on the basis of resistance torques, etc.; and if a tendency to slip occurs at at least one drive wheel, the torque of the drive unit of the vehicle is reduced in such a way that the maximum transmittable drive output torque is implemented.
The limitation or reduction, according to the present invention, in the torque of the drive unit of the vehicle when oscillations occur effectively suppresses those oscillations and thereby improves vehicle comfort. By way of the reduction in torque by correspondingly influencing the setpoint for controlling the drive unit, which depends substantially on the driver, the cause of drivetrain oscillations is influenced. This is because drivetrain oscillations occur as a function of driver behavior when the driver performs a load change, and in particular accelerates by rapid actuation of the accelerator pedal.
It is advantageous that the reduction is performed until the oscillations decay, so that laborious actions that react to individual oscillations can be dispensed with.
It is particularly advantageous that the setpoint value at which the oscillation has occurred is stored; and in a later situation, when that value is exceeded, a limitation of the torque change is performed even without recognition of a drivetrain oscillation. This effectively prevents the occurrence of oscillations.